1. Field of the Invention
The present invention generally relates to methods and systems for monitoring electric power distribution system components distributed in a plurality of locations. In particular, the invention concerns the monitoring, in real time and by exploiting optical fibers, of the state and condition of “ancillary” elements, for example protection elements used in electric power distribution systems for ensuring the system security.
2. Description of Related Art
Distribution systems of electric power comprise distribution networks, for example high voltage (HV) distribution networks.
The term “high voltage” is related to voltages higher than 35 kV, reaching also one or more hundreds of kilovolts.
The distribution networks make use of cables that may, for example, be aerial (overhead) or underground, for example positioned in tunnels.
In addition to cables, distribution networks can comprise a number of different ancillary elements that, strictly speaking, do not play a direct role in the electric power distribution, being instead used to guarantee proper conditions of usage and security of the distribution line.
Examples of ancillary elements are surge voltage limiters (SVLs), also known as surge arresters (SAs) or surge suppressors, oil pressure monitoring systems for oil-filled cables, thermometers to check the pumps for circulating cooling water and the cooling water temperature itself.
The monitoring and the maintenance of the ancillary elements of a cable, in view of the environment where the cables are located, which can be either critical, because recessed, and/or dangerous, like in the case of HV networks, may be cumbersome, and cannot be effected on a frequent time basis. Even when the ancillary elements are not enclosed in protective boxes, the monitoring of their operating conditions can imply long inspections and/or the interruption of the distribution of the electric power.
This is indeed strongly undesired, because an electric power distribution line normally supplies a very large area and a substantial number of users, which are never ready to accept a service interruption.
There is therefore the need of devising a solution to the problem of monitoring the proper operation of ancillary elements like SVLs, oil pressure monitoring systems, thermometers with the aim of being able to replace them as readily as possible when they break.
In the published Japanese patent application JP 04-092523, a detecting sensor for contact information is described, to detect the contact information with no mechanical force applied. Light shading mechanisms are provided and operate by the contact information between optical branches devices and mirrors provided at plural areas of an optical fibers.
The Applicant observed that said shading mechanisms are of the active type, i.e. require an outer energy source to operate, particularly, in the examples provided, an electric power supply. No application to power cables is envisaged
In the published Japanese patent application JP 2004309219, a sensor measuring system is disclosed, comprising a plurality of fiber measuring sensors for measuring a number of physical quantities.
The Applicant observes that the sensors are positioned in series on a main optical fiber, not on the branching thereof, therefore intensity reduction in one of them lessens the amount of light available in the following sensors, thereby reducing the measurement dynamics.
In the published Japanese patent application JP 03-231116, an optical fiber sensor is disclosed wherein fiber end faces of multiple branched optical fibers are inserted into oil, and pulse light is inputted from a reflection measuring device like an optical time domain reflectometer (OTDR); Fresnel reflection at the fiber end is therefore attenuated and so the event detected.
The published U.S. patent application 2004/0240769 describes an alarm condition distributed fiber optic sensor with storage transmission-reflection analyzer. The Applicant observed that both transmission and reflection detectors are electrically connected to the storage transmission-reflection analyzer.
The U.S. Pat. No. 5,035,511 describes a distributed fiber optic temperature sensor based on time domain transmission. Light is transmitted through the sensor only one time, and not reflected back.